1. Field of the Invention
The present invention relates generally to clamping apparatuses for injection molding machines and, more particularly, to a five-joint clamping apparatus for an injection molding machine which retains the advantages of a conventional five-joint clamping apparatus, specifically, high mold opening or closing speed and control precision, has an increased stroke distance in link mechanism, and has a structure capable of pressing a central portion of a mold.
2. Description of the Related Art
Injection molding machines are apparatuses for forming products of synthetic resin material or the like. Generally, injection molding machines form products in such a way as to melt chips or powder and put it into a mold having a predetermined shape. There are various kinds of injection molding machines, from small sized machines to large sized machines. Polyester, vinyl acetate, different kinds of plastics, nylon, etc. can be used as material for forming products using the injection molding machines.
Such injection molding machines are classified into hydraulic injection molding machines and electric injection molding machines. In conventional techniques, hydraulic injection molding machines have been widely used.
Among hydraulic injection molding machines, a direct pressure type injection molding machine, in particular, has an advantage of a simple structure, being configured such that a mold is opened or closed by a cylinder.
However, the hydraulic injection molding machine requires consumption of a large amount of working fluid, inducing disadvantages of causing environment pollution and being difficult to maintain and repair.
As the above disadvantages of the hydraulic injection molding machine are magnified, electric injection molding machines, which are configured such that operation thereof including mold closing or opening operation is enabled by a servo-motor, are being more widely used.
Among the electric injection molding machines, toggle type injection molding machines are mainly used.
The electric injection molding machines require, in terms of maintenance, only the lubrication of toggle links, are able to reduce energy consumption by up to 80%, and markedly reduce the possibility of environment pollution because working oil is not used.
The injection molding machines are apparatuses which conduct injection molding operation after mold closing force has been applied to a mold between a movable plate and a stationary plate using tie bars.
As stated above, toggle type injection molding machines are mainly used as the electric injection molding machines and are operated in such a way that, while a mold is interposed between a movable plate and a stationary plate, as links are stretched, pushing force applied to the mold is increased, thus generating the mold closing force and increasing it.
For this, the injection molding machines include a clamping apparatus. Clamping apparatuses of the toggle type injection molding machines are classified into a single toggle type clamping apparatus including a pair of toggle links, and a double toggle type clamping apparatus including two pairs of toggle links.
The single toggle type clamping apparatus is suitable for a small injection molding machine. The double toggle type clamping apparatus is suitable for an injection molding machine that requires comparatively mold closing force.
Double toggle type clamping apparatuses are classified into a four-joint type and a five-joint type according to a structure of connecting a toggle link to a crosshead link.
The four-joint clamping apparatus is configured such that a crosshead link, a long link and a short link are connected together by a single joint.
The four-joint clamping apparatus is advantageous in that comparatively large mold closing force can be generated using relatively small input force, because mechanical advantage is large.
However, in the four-joint clamping apparatus, a displacement of the crosshead is comparatively large during a mold opening or closing stroke. Therefore, a mold opening speed is low, and the size of the clamping apparatus is increased.
To overcome the problems of the four-joint clamping apparatus, the five-joint clamping apparatus was proposed.
The five-joint clamping apparatus is configured such that a joint of connecting a crosshead link to a short link is provided separately from a joint of connecting a long link to the short link.
In the five-joint clamping apparatus, the crosshead link 112 is connected to the short link 108 at a joint E1 which forms a smaller radius of rotation based on a joint B1 than does a joint A1. Compared to the four-joint clamping apparatus in which the crosshead link 112 is connected to the joint A1, the speed of a mold opening or closing stroke is increased, and the length of the clamping apparatus can be reduced because of reduced displacement of the crosshead 111.
Furthermore, the conventional five-joint clamping apparatus has an inward-folding and inner-joint type toggle link structure in which a toggle link is folded inwards and a link coupling part is fixed to an inner joint (refer to FIG. 2). Such an inward-folding and inner-joint type toggle link structure is advantageous in that it is suitable for a typical toggle link structure that is operated at high speed.
However, in the inward-folding and inner-joint type toggle link structure, the maximum stroke distance of the movable plate is 540 mm, and it is very difficult to further increase the stroke distance.
Meanwhile, to improve the conventional inward-folding and inner-joint type toggle link structure, an improved toggle link structure was proposed in U.S. Pat. No. 5,843,496 (hereinafter, referred to as conventional technique 1) in which a link coupling part is fixed to an outer joint.
Conventional technique 1 provides an inward-folding and outer-joint type toggle link structure, in which the area the links take in the injection molding machine is reduced and efficiency of mold clamping force generation is enhanced, compared to the inward-folding and inner-joint type toggle link structure.
The inward-folding and outer-joint type toggle link structure according to conventional technique 1 has advantages of improved efficiency in generating mold clamping force and being capable of more smoothly applying mold clamping force to a mold. However, it still has problems of difficulty in achieving a long stroke distance, that is, increasing the stroke distance, and difficulty in embodying high-speed operation.
Typically, in the case of the electric injection molding machines, toggle type injection molding machines are mainly used. In such a toggle type, links are connected to a perimeter of a movable plate rather than to a central portion thereof.
Therefore, during a mold closing operation, the links press the perimeter of the movable plate, thus markedly increasing the possibility of the mold being deformed compared to that of the direct pressure type injection molding machine. Furthermore, it is very difficult for the toggle type injection molding machines to realize a center pressing structure such that force is applied to central portion of the movable plate.